As First Lady, Nancy Reagan, who died yesterday at 94, was a deft international ambassador for brisk, polished, and generally faultless American high style.

A birdlike 5-foot-4 and a size 2, Mrs. Reagan learned her sartorial lessons as an MGM contract player in the studio’s fabled costume fitting rooms. As First Lady, she chose her clothes for their cinematic—or rather, telegenic possibilities—suavely selecting simple lines that would showcase her figure, and silhouettes that would not overpower her. “I don’t like a lot of frills and fusses,” she told W in 2007, “I’ve always gone for the more understated look.”

Nancy Reagan took some cues from Jacqueline Kennedy’s First Lady playbook, notably in her preference for strong color, including her signature Reagan red (“I always liked red. It’s a picker-upper,” she noted), or gleaming, often crystallized white that made her diminutive figure instantly identifiable in a crowd.

Nothing could have proclaimed the dawning of the age of unabashed conspicuous consumption more than the Reagans’ arrival to the White House. In later life, the diplomatic Nancy would admit that she considered the White House the Carters had left “shabby.” She summoned Ted Graber, the protégé and boyfriend of William Haines (erstwhile Hollywood heartthrob turned decorator to the stars and to Hollywood royalty including Alfred Bloomingdale and Sidney Brody), to affect a glamorizing makeover. Graber brought the California sunshine and a sense of Bel Air luxe to the private quarters, and sparkling grandeur to the staterooms. The Reagans’ entertaining was scaled to match: They hosted 56 state dinners in eight years (George and Laura Bush, in contrast, hosted six). “My, the White House is very grand,” confided the queen’s sister Princess Margaret to her friend Carolina Herrera during a visit.

Rosalynn Carter’s earnest clothing choices had been characterized by a folksy lack of pretension. For her 1977 inaugural gown, for instance, she chose to wear a faintly I Dream of Jeannie ensemble that she had worn six years earlier to her husband’s inauguration as governor of Georgia, and carried with it a faint whiff of hippie-era exotica.

Nancy Reagan heralded an altogether different era when she commissioned her old friend James Galanos (whom she had met in 1949, at the outset of his career), to make her own 1981 inaugural gown; a one-shouldered white sheath hand-embroidered in feathery curlicues of crystal beads that she wore with opera-length white kid gloves and her hair in a French pleat. Galanos also made her 1985 gown, this time lavished with a rumored 300 hours’ worth of embroidery. But although she was much criticized for her extravagant spending, Nancy Reagan could be thrifty too. “Nobody could afford to dress completely with Jimmy,” Mrs. Reagan once noted of Galanos’s fabled prices, “I hang on to what I have.” In fact, she wore a 14-year-old Galanos to the first Reagan state dinner.

The criticism leveled at her could be scalding, but Nancy Reagan fought back with the astute diplomacy with which she guided her husband’s presidency. At a white-tie dinner for 600 guests at the annual Gridiron Club in 1982, Nancy Reagan’s clotheshorse image was the butt of the roast. She excused herself at some point in the proceedings, and there was a feeling that she had left in high dudgeon, but to the surprise of all, including the President himself, she reappeared on-stage dressed in mismatched floral tat (that bears an uncanny resemblance to the floral numbers in Demna Gvasalia’s debut Balenciaga collection), and performed the rest of the skit herself. She brought the house down.

Nancy Reagan not only embraced fashion on her own terms, she counted a number of designers among her friends, and welcomed many of them to the White House. (The Kennedys had entertained Oleg Cassini, of course, but he was an old family friend.) For creators like Bill Blass and Geoffrey Beene, who had begun their careers as backroom boys, working anonymously for Seventh Avenue manufacturers, this was a vindication of their status as creative talents.

“What better endorsement for our industry,” noted Oscar de la Renta, another great designer friend, “than to have a wonderfully well-dressed First Lady?” Nancy Reagan was honored by the CFDA in 1988 with a Lifetime Achievement Award—it was presented to her by her old friend Brooke Astor, reigning doyenne of Manhattan society.

I was so struck by Mrs. Reagan’s fashion legacy that in 2008 I made a pilgrimage to the Reagan Library, a sprawling behemoth of a building atop a hill in Simi Valley in the scrubby Californian desert, lured by the recently inaugurated exhibition “Nancy Reagan: A First Lady’s Style,” showcasing some 80 ensembles that defined her taste, arranged in a decor evocative of the majesty of the White House staterooms. The precision and coherence of her wardrobe choices through the decades were striking, from the unadorned, shapely white-collared gray wool suit from I. Magnin that she wore to marry Ronald Reagan in 1952, to the clothes that defined her years as First Lady, and there was a poignancy to the care with which she had cherished and preserved them.

Although a symbol of the Dynasty era Shiny Set, with her famed “Kitchen Cabinet” of glamorously dressed, ageless West Coast tastemakers, Nancy Reagan acknowledged trends but adapted them to her own purpose.

“She was always immaculate,” Jimmy Galanos remembered, but “if I tried to experiment,” as he noted to the L.A. Times, “I could tell from her expression that she was thinking, ‘No, Jimmy.’ ” Her one experiment—beaded Galanos knickerbockers, worn to the American Embassy in Paris—was not considered her finest sartorial hour.